Saudi Arabia's attorney general sought the death penalty for five of 11 defendants charged with the murder of journalist Jamal Khashoggi as their high-profile trial opened in Riyadh on Thursday.

All 11 accused were present with their lawyers at the opening hearing in the capital, according to a statement by the attorney general carried by the official Saudi Press Agency.

The attorney general said Saudi Arabia had twice submitted formal requests for evidence from Turkey — where Khashoggi was murdered inside the kingdom's Istanbul consulate — but had received no response.

The names of the 11 defendants have not been officially released.

Khashoggi, a contributor to the Washington Post, was murdered on October 2 in what Riyadh called a "rogue" operation.

The 59-year-old Saudi insider-turned-critic was strangled and his body cut into pieces by a team of 15 Saudis sent to Istanbul for the killing, according to Turkish officials.

There have been reports that his remains, which have never been found, were dissolved in acid.

The consulate and the residence were searched by the Turkish authorities in October along with several other locations.

Ankara has sought the extradition of the suspects in Saudi custody to stand trial in Turkey but its requests have been repeatedly rebuffed by Riyadh.

The US Central Intelligence Agency has reportedly concluded that the kingdom's de facto leader, Crown Prince Mohammed bin Salman, very likely ordered Khashoggi's murder.

But in November the Saudi attorney general ruled out any involvement by the young crown prince, whose reformist credentials abroad have been seriously tarnished by the killing.